In the magnetic switch of an automotive starter motor, an plunger is driven by selectively supplying electric current to an energization coil, and the resulting movement of the plunger shifts a pinion gear into mesh with a ring gear. A plate-shaped moveable contact member is integrally secured to a rod which is moved by the movement of the plunger, and the motor is electrically connected to a battery by selectively contacting this contact member across a pair of fixed contact members.
In such a magnetic switch, when the switch is closed, a relatively large current flows through the switch, and the temperature of the contact surface tends to rise as a result of this electric current, thereby increasing the contact resistance and impairing the efficiency of the switch. Japanese utility model laid open publication No. 53-155060 discloses a contact assembly in which the contact surface is provided with a surface irregularity, and the state of contact is made stable by preventing slippage at the time of contact. By thus providing a surface irregularity in the contact surface, the effective surface area for heat dissipation is increased, and the heat is more efficiently removed from the contact surface.
To optimize the efficiency of heat dissipation, each projection in the irregular contact surface is required to be separated from other projections. However, forming such surface irregularities will require punches having highly complex configurations, and it will increase the fabrication cost.